1. Field of the Invention
The present invention relates to the production of xylylenediamines by the hydrogenation of phthalonitriles. Xylylenediamines are useful compounds as the raw materials for polyamide resins, curing agents, etc. and as the intermediates for isocyanate resins, etc.
2. Description of the Prior Art
The production of xylylenediamines by the hydrogenation of phthalonitrile in the presence of a heterogeneous catalyst in a continuous flow reactor has been well known. For example, a liquid-phase catalytic hydrogenation of phthalonitriles in the presence of a nickel-copper-molybdenum-containing catalyst is disclosed in JP 53-20969A. The hydrogenation is carried out using a fixed-bed continuous flow reactor in the working examples of JP 53-20969B. In another method, phthalonitriles obtained by the ammoxidation of xylylene are collected in an organic solvent, and then, after adding liquid ammonia without separating phthalonitriles, the collected phthalonitriles are continuously hydrogenated into corresponding xylylenediamines in a trickle bed reactor packed with a nickel and/or cobalt-containing catalyst (JP 2002-105035A). In still another method, isophthalonitrile obtained by the ammoxidation of m-xylylene is collected in an organic solvent, and then, the isophthalonitrile separated by distillation is continuously hydrogenated into corresponding m-xylylenediamine in a mixed solvent of liquid ammonia and hydrocarbon solvent in a trickle bed reactor packed with a nickel and/or cobalt-containing catalyst (JP 2003-26639A).
In another known method, phthalonitriles are hydrogenated to xylylenediamines in the presence of a heterogeneous catalyst using a continuous flow reactor while circulating a part of the reaction product solution from the continuous flow reactor to the inlet of the reactor (hereinafter referred to as “circulation method”). In GB 852972, it is taught that the circulation of the hydrogenation product solution as the solvent is advantageous in the hydrogenation of phthalonitriles to xylylenediamines in the presence of a cobalt-containing catalyst, and a production of m-xylylenediamine in the presence of a cobalt-manganese-containing catalyst using a fixed-bed continuous flow reactor is proposed in which the hydrogenation product solution is reused as a part of the solvent. The hydrogenation of nitrites to amines in the present of a cobalt-containing catalyst is known, and GB 1143890 discloses the production of m-xylylenediamine by the circulation method in the presence of a cobalt-manganese-containing catalyst. In still another known method of producing xylylenediamines by the hydrogenation of phthalonitriles in liquid ammonia in the presence of a heterogeneous catalyst, molten phthalonitriles are dissolved in a hydrogenation product solution circulated as a part of the solvent and then fed to a fixed-bed continuous flow reactor for hydrogenation. It is taught that the selectivity is enhanced and the amount of liquid ammonia used can be reduced by the circulation of the hydrogenation product solution (WO 2005/026098).
It has been found, however, that the reaction intermediate such as cyanobenzylamines is likely to remain unchanged in the circulation method because of a reduced reaction rate. Cyanobenzylamines are required to be removed by separation, because it impairs the properties of resins, etc. However, it is difficult to separate cyanobenzylamines from xylylenediamines because of a small difference in their boiling points. The removal of cyanobenzylamines by amidation is disclosed in JP 56-2941A. However, the disclosed method requires a complicated apparatus and reduces the yield of xylylenediamines from phthalonitriles.
To solve the above problems, the hydrogenation should be completed as much as possible. However, a larger reactor and an increased amount of catalyst should be required for the completion of hydrogenation, making the process industrially disadvantageous.